1. Field of the Invention
The present invention relates to a thrombectomy method and apparatus for removing a soft, newly formed thrombus or blood clot from a blood vessel, and particularly to the application of an obstruction dissolving agent into the fibers of the obstruction as the fibers are mixed and exposed by a soft, flexible rotating brush for fragmenting and dissolving the fragments of the obstruction in situ.
2. Description of the Background Art
The acute symptoms of blockage of a vein at a venous valve or a partially sclerosed and narrowed artery may be instigated by the presence of a soft blood clot which may either form at the site or form elsewhere, as through trauma or injury to the vascular system, at a cardiac valve or at the site of an access fistula for enabling chronic hemodialysis and be carried to the site by the flow of blood. In the venous and arterial blood vessels, such clots are referred to as an embolus or emboli and a thrombus or thrombi, respectively. Emboli and thrombi are characterized by a soft consistency that maintains a form and is resistant to dissolution in the bloodstream or in water and entraps red blood cells. Under the microscope it can be seen that this clotting behavior is effected by strands of fibrin which are formed of normally soluble fibrinogen molecules which undergo a conversion to stranded fibrin in response to a chemical released at the site of an injury to a blood vessel wall in order to prevent the loss of blood through the injured wall. Recently formed blood clots stabilized in position as emboli and thrombi are soft and jelly-like in consistency and are readily penetrated but reform after the penetrating object is removed.
The invasive removal of both soft and hard obstructions from arteries and prostheses implanted to substitute for diseased arteries or to retain arteries open to blood flow has become commonplace. Over many years, a patient's arterial system may become narrowed and eventually occluded with relatively hard, calcified plaque resulting in reduced blood flow and consequent oxygen deprivation, to organs and muscles supplied by the arterial system. The progress of atherosclerosis in a given patient may not be diagnosed until the onset of an ischemic episode triggering the symptoms of chest pain or heart failure, with respect to cardiac arteries, or a stroke or eyesight failure, if the carotid artery or its tributaries are blocked. Usually, the cardiac arteries in patients that suffer ischemia and have become blocked slowly over the years develop collateral blood vessels that take over or share the burden of supplying oxygen to the myocardium. However, as the disease is progressive, the arterial system eventually becomes incapable of sustaining that burden resulting in myocardial infarction. In the peripheral arteries, a blockage of oxygen carrying blood may cause pain or the onset of gangrene resulting in amputation of the limb or eventual death.
When blockage takes place, the patient is at risk of death or serious myocardial infarction or paralysis unless the blockage is promptly eliminated. Once diagnosed, treatments are first undertaken to remove the soft obstruction and restore the blood flow. Once the soft obstruction is removed, drug therapy may be instituted and the patient may undergo coronary artery bypass graft surgery to replace the occluded cardiac arteries with vein sections sacrificed from the patient's peripheral venous system or with artificial grafts. Alternatively, the occlusions in the arteries may be expanded through balloon angioplasty, and artificial stents may be implanted to brace the expanded arterial wall. Other techniques for removing the obstruction occluding the vessel include invasively abrading or cutting away the built up placque and aspirating the fragments out of the bloodstream with mechanical atherectomy tools are described in U.S. Pat. No. 4,842,579 to Shiber. In addition catheter systems employing laser energy are also being clinically used. In the carotid artery, the occlusion may have to be excised by surgical endorevectomy.
With respect to the venous system, emboli may collect at constrictions or valves in the relatively slow moving bloodstream. Emboli obstructing major venous valves creates a back pressure in the circulatory system so as to reduce blood flow even in the arterial system. Trapped venous blood causes swelling of the limb and the combination of swelling and reduced arterial blood flow may itself threaten the viability of the limb. Treatment for this condition involves long term use of anti-coagulation drugs to attempt to reduce the formation of new emboli.
The acute treatments that are undertaken to remove thrombi or emboli take many forms. At the onset of serious symptoms, the site of obstruction is identified with radiographic agents introduced into the bloodstream in a diagnostic radiographic procedure of the type described in my U.S. Pat. No. 5,085,635. Then dissolving agents, e.g. streptokinase or urokinase, may be infused through catheters which are introduced into the venous system and advanced until the infusion port at the distal end of the catheter is situated adjacent to the blockage. The dissolving agent is infused slowly over a matter of hours while the patient is monitored. At safe low dosages, this procedure is time consuming and requires careful monitoring of the risk of bleeding.
Other treatments have been proposed for mechanically entrapping and removing stabilized thrombi, including the use of the "Fogarty catheter" or inflatable balloon embolectomy catheter of the type disclosed in U.S. Pat. No. 3,435,826 to Fogarty. Typically, the balloon catheter is guided with the balloon collapsed through and into a location distal to the thrombus. The balloon is expanded and withdrawn in order to dislodge the thrombus and pull it along and out the incision in a blood vessel. In using this procedure, a risk exists that all or a portion of the thrombus will dislodge and travel to a further restriction in the arterial system.
Various other embolectomy/thrombectomy catheters and methods have been proposed, including the use of an elastomeric foam at the distal tip, rather than an expandable balloon, as disclosed in U.S. Pat. No. 5,192,290 to Hilal. In U.S. Pat. No. 4,646,736 to Auth, it is proposed that a coiled wire be passed through a blood clot and rotated to catch and wind the fibrin structure while withdrawing blood or introducing a dissolving agent, e.g. streptokinase. In U.S. Pat. No. 4,692,139 to Stiles, it is proposed to employ the combination of ultrasound and a dissolving agent infused into a blood clot to emulsify and fragment the fibrin structure of the clot and to aspirate the fragments.
In use of such equipment, it is not possible to determine if the entire thrombus has been trapped or all fragments have been aspirated. Employing various techniques, accelerated atherosclerosis or internal hyperplasia has been reported at the removal site.
Despite the advances and improvements in treatment that have been introduced in recent years, a need remains for an embolectomy/thrombectomy apparatus and method that is simple to practice, does not threaten the integrity of the vessel, and wherein the vessel patency is rapidly restored.